1. Field of the Invention
This invention relates to integrated circuits, and more particularly, to the testing of 3-dimensional memory arrays implemented on an integrated circuit.
2. Description of the Related Art
Various types of memory arrays may be implemented on microprocessors and other types of integrated circuits. One type of memory array commonly used is a 3-dimensional (3D) memory array. A 3D memory array includes an active array and a static array. The active array includes both read and write ports, while the static array typically includes only a write port. Information may be written to the active area or read directly therefrom. In contrast, information cannot be directly read from the static array. Instead, reading the contents of the static array requires that data be transferred from the static array (via a transfer mechanism) to the active array, from which it is subsequently read.
Applications utilizing 3D memory arrays include storing thread-related information in multi-threaded processors and the storage of register history in processors configured for speculative execution, among others. In the first of these two applications, information pertaining to an active thread is stored in the active array, while information pertaining to a currently inactive thread is stored in the static array, to be transferred to the active array when the inactive thread becomes active. In the second of these two application, register file history may be stored in the static array and transferred to the active array if it is necessary for the processor to back up to a previous state (e.g., due to a branch misprediction).
Due to their organization, the testing of 3D memory arrays poses special problems. Since the static array of a 3D memory array does not have a read port, conventional memory tests cannot be performed. For example, many types of March tests (e.g., MATS, MATS+, MATS++, MarchC, MarchC-, MOVI, etc.) that are well known in the art require a write cycle immediately followed by a read cycle, followed by another write cycle immediately following the read cycle, and so forth. However, since data cannot be read directly from the static array, these tests cannot be performed in their conventional manner.